JP7200751B2 - power supply - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply, and more particularly to a rush current prevention circuit that suppresses rush current to a smoothing capacitor.

2. Description of the Related Art Conventionally, a power supply device equipped with an inrush current prevention circuit is provided in an inverter device 100 shown in FIG. In this inverter device 100, a voltage output from a fuel cell 102 is input to a booster circuit 104. The booster circuit 104 boosts the input voltage and supplies it to an inverter 105. The inverter 105 boosts the input voltage. After being converted into a three-phase power supply, it is output to the motor 109 .

The inverter device 100 also includes a main relay 103 in series between the fuel cell 102 and the booster circuit 104 . A smoothing capacitor 101 is connected in parallel with a booster circuit 104 between two output terminals. In rush current prevention circuit 110, resistor 107 and auxiliary relay 106 are connected in series.

Control circuit 108 opens both main relay 103 and sub-relay 106 when motor 109 is stopped. Then, the control circuit 108 closes the sub-relay 106 before rotating the motor 109, and causes a current (rush current) to flow through the smoothing capacitor 101 via the resistor 107 to raise the voltage of the smoothing capacitor 101 to a predetermined voltage. . Control circuit 108 then closes primary relay 103 and then opens secondary relay 106 .

Then, control circuit 108 operates booster circuit 104 to boost the input voltage and supply it to inverter device 100 . Next, the control circuit 108 operates the inverter 105 to rotate the motor 109 .

By the way, the contact current of a mechanical relay is specified in the specifications, and by limiting this current to within the specified contact current, it is possible to prevent the contacts from welding due to the inrush current that flows when the relay is closed. It has become. Therefore, if the capacity of the smoothing capacitor 101 is fixed and an inexpensive secondary relay 106 with a small contact current is to be used, the value of the resistor 107 must be increased to keep the inrush current below the contact current. Naturally, in this case, it takes longer for the voltage of the smoothing capacitor 101 to rise to the predetermined voltage, and there is a problem that it takes longer for the motor 109 to start rotating.

On the other hand, in order to shorten the time required for the voltage of the smoothing capacitor 101 to rise to a predetermined voltage, it is necessary to employ the auxiliary relay 106, which has a large contact current and is expensive, resulting in an increase in cost. Furthermore, in this case, since the inrush current becomes large, it is necessary to select the parts in the booster circuit 104 and the smoothing capacitor 101 that are capable of withstanding this large inrush current, which further increases the cost.

This problem can be solved by closing the secondary relay 106 when the current flowing through the secondary relay 106 is minimal. For example, in the case of an AC power supply in which a rectified AC voltage is applied to the inrush current prevention circuit 110 instead of the fuel cell 102 in FIG. What is necessary is to prevent a sudden large current from flowing when the auxiliary relay 106 is closed. In other words, this problem can be solved by performing so-called zero voltage switching.

However, mechanical relays have a mechanical delay time from when the control signal is input until the contacts close, but this delay time varies depending on the characteristics of individual relays, aging, driving voltage, ambient temperature, etc. do. Therefore, even if a relay with a small contact current standard is used to control the contact of the auxiliary relay 106 to close at the zero-crossing point of the AC voltage, the contact cannot be closed at the target timing due to fluctuations in the delay time. There was a case where an inrush current larger than the contact current standard of the relay flowed.

Japanese Patent Application Laid-Open No. 2005-261040 (paragraph numbers 0014 to 0021)

The present invention solves the problems described above, and in a power supply device that rectifies an AC power supply, when a mechanical relay used in an inrush current prevention circuit that suppresses inrush current flowing through a smoothing capacitor is closed, zero voltage switching is achieved. The purpose is to ensure that

In order to solve the above problems, the invention according to claim 1 of the present invention is
A pair of input terminals to which an AC power supply is connected, a rectifier for rectifying the AC voltage applied to the input terminals, a smoothing capacitor for smoothing the rectified voltage,
inrush current prevention means connected in series between one of the pair of input terminals and the rectifier to suppress inrush current flowing through the smoothing capacitor;
A power supply device comprising a control unit that outputs a control signal for opening and closing the relay to the inrush current prevention means,
The inrush current prevention means is
A mechanical relay, a diode, and a resistor connected in series between one of the pair of input terminals and the rectifier, and detecting the polarity of the AC voltage applied to the pair of input terminals as a polarity signal and a voltage polarity detection unit that outputs
The inrush current prevention means is
When the control signal for closing the relay is input,
The relay is delayed by a predetermined time from the zero cross point detected by the polarity signal so that the timing at which the contact of the relay is closed is within the period of the polarity of the AC voltage that becomes the reverse voltage in the diode. is output to the relay to close the drive signal.

By using the above-described means, according to the power supply device of the present invention, the inrush current prevention means closes the relay during a period in which no current flows through the diode connected in series with the relay. Inrush current can be reduced. Therefore, it is possible to employ a relay with a smaller contact current than the relay used in the conventional inrush current prevention circuit system.

1 is a block diagram showing an embodiment of a power supply device according to the present invention; FIG. It is an explanatory view explaining operation of a power supply device by the present invention. 1 is a block diagram showing a conventional power supply; FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail as examples based on the accompanying drawings.

FIG. 1 is a block diagram showing an embodiment of a power supply 30 according to the invention. The power supply device 30 includes an input terminal 1a and an input terminal 1b, which are a pair of input terminals to which a 50 Hz AC power supply (not shown) is connected, an output terminal 6a and an output terminal 6b for outputting a DC voltage, and an input terminal 1a. A rectifier 2 connected between the input terminals 1b for rectifying the output voltage of the AC power supply, a smoothing capacitor 7 connected between the output terminals 6a and 6b for smoothing the output voltage of the rectifier 2, and an input terminal 3e. and an input terminal 3h, an output terminal 3f and a common terminal 3g, and a control section 5 for outputting a switching pulse signal for driving the switching section 3 to the input terminal 3h.

The input terminal 3e of the switching section 3 is connected to the output positive terminal of the rectifier 2, and the common terminal 3g of the switching section 3 and the negative terminal of the smoothing capacitor 7 are connected to the output negative terminal of the rectifier 2, respectively. A main relay 4 is connected in series between the input terminal 1a and one end of the rectifier 2 on the input side. The control unit 5 also opens and closes contacts of a sub-relay, which will be described later.

On the other hand, the switching unit 3 includes an inductor 3a having one end connected to the input terminal 3e, a diode 3b having the other end connected to the anode terminal of the inductor 3a and the cathode terminal connected to the output terminal 3f, and the inductor 3a. An IGBT 3c, which is a switching element connected between the end and the common end 3g and turned on/off by an input switching pulse signal, is provided. The IGBT 3c has a collector terminal connected to the other end of the inductor 3a, an emitter terminal connected to the common terminal 3g, and a gate terminal connected to the input terminal 3h.

In this switching unit 3, an IGBT 3c is connected between the output-side positive electrode and the output-side negative electrode of the rectifier 2 via an inductor 3a. In the switching unit 3, when the IGBT 3c is short-circuited, a current flows through the inductor 3a and is stored as energy, and when the IGBT 3c is opened, the stored energy becomes a current and flows from the inductor 3a into the smoothing capacitor 7, resulting in It has a step-up function to increase the voltage of the smoothing capacitor 7 as a matter of course.

On the other hand, between the input terminals 1a and 1b and the rectifier 2, an inrush current prevention circuit (inrush current prevention means) 20 for suppressing inrush current to the smoothing capacitor 7 is provided. The inrush current prevention circuit 20 includes an auxiliary relay (mechanical relay) 25, a diode 24, a resistor 26, and an input terminal 1a, which are connected in series between the input terminal 1a and one input side of the rectifier 2. A voltage polarity detection unit 21 that detects the polarity of the AC voltage applied between the input terminals 1b and outputs it as a polarity signal, and an auxiliary relay signal (control signal) output by the control unit 5 and output from the voltage polarity detection unit 21 and an AND circuit 23 for outputting a trigger signal which is the logical product of these signals, and an AND circuit 23 for delaying the input trigger signal by a predetermined time, 5 milliseconds in this embodiment, to open and close the auxiliary relay 25. A delay circuit 22 is provided for outputting a drive signal to be performed. The diode 24 is connected in such a direction that a current flows when a positive half cycle of AC voltage is applied to the input terminal 1a.

Next, the operation of the power supply device 30 will be described.
Before the power supply device 30 outputs the DC voltage, both the main relay 4 and the sub-relay 25 are open, and the IGBT 3c is also off. After AC power is connected to the input terminals 1a and 1b, the control unit 5 first sets the auxiliary relay signal to a high level to charge the smoothing capacitor 7. FIG. The power supply device 30 includes a control DC power supply (not shown). AC power is input to the control DC power supply from the input terminal 1a and the input terminal 1b. and a DC control power supply such as +5 volts or +12 volts to the inrush current prevention circuit 20 .
Further, in this embodiment, since the power supply unit is explained as a single unit, the trigger for closing each relay is explained as when the AC power supply is turned on. An instruction from the device, for example, an instruction to start rotation of a compressor in an air conditioner may be used.

A high-level auxiliary relay signal is input to one input terminal of the AND circuit 23 of the rush current prevention circuit 20 . On the other hand, the voltage polarity detector 21 outputs a polarity signal of high level when the AC voltage is in the positive half cycle and low level when it is in the negative half cycle. The AND circuit 23 outputs to the delay circuit 22 a trigger signal that changes from low level to high level when the AC voltage becomes positive half cycle for the first time after the sub relay signal becomes high level. The delay circuit 22 delays the input signal by 5 milliseconds before outputting it to the auxiliary relay 25 as a drive signal.

The auxiliary relay 25 has a mechanical delay time from when the control signal is input until the contact is closed, and even if the drive signal changes from low level (open) to high level (closed) The contacts of the auxiliary relay 25 are not actually connected until this mechanical delay time elapses. In addition, since this mechanical delay time varies due to various factors as described in the background art, the sub-relay 25 of this embodiment has a specification of this mechanical delay time of 10 milliseconds±1.5 milliseconds. However, the variation range may increase further depending on aging and the surrounding environment.

In this embodiment, since the frequency of the AC power supply is 50 Hz, the low level secondary relay signal becomes high level, and the predetermined time from the first positive half cycle of the AC voltage: 5 milliseconds and the secondary relay After 15 milliseconds plus 25 mechanical delay times, the contacts of secondary relay 25 are actually closed. This timing is 5 milliseconds after the AC voltage goes into the negative half cycle and is in the middle of the negative half cycle.

Since this negative half period is a reverse voltage period during which no current flows through the diode 24, no current flows through the contacts of the auxiliary relay 25 when they are actually connected. In addition, since no current flows for a period of 5 milliseconds before and after the center of this negative half cycle, even if the mechanical delay time of the auxiliary relay 25 fluctuates, if it is within this negative half cycle period, the contact will not be applied. no current flows. In addition, even if chattering occurs in the contact within the period of this negative half cycle, current does not actually flow.

FIG. 2 is an explanatory diagram for explaining the operation of the power supply device 30 including the inrush current prevention circuit 20 according to this embodiment.
The horizontal axis of FIG. 2 is time, and with respect to the vertical axis, FIG. 2(1) is the 50 Hz AC voltage, FIG. 2(2) is the output voltage of diode 24, FIG. 2(4) is the sub-relay signal, FIG. 2(5) is the drive signal, FIG. 2(6) is the contact state of the sub-relay 25, and FIG. FIG. 2(8) shows the current flowing through the rectifier (in the case of using the conventional circuit), respectively. Note that t0 to t9 are times.

As shown in FIG. 2(1), the AC voltage has one cycle, for example, a positive half cycle of 10 milliseconds indicated by t2 to t4 and a negative half cycle of 10 milliseconds indicated by t4 to t7. . Further, as shown in FIG. 2(2), at the timing when the sub-relay 25 (to be described later) is closed and during the positive half cycle of the AC voltage, the cathode terminal of the diode 24 is closed only during the period from t7 to t9, for example. The output voltage appears at . Also, as shown in FIG. 2(3), the polarity signal changes from a low level to a high level when the AC voltage switches from the negative half cycle to the positive half cycle, and switches from the positive half cycle to the negative half cycle. Sometimes it goes from high level to low level. Therefore, these switching timings, for example, t2, t4, t7 and t9, are zero crossing points.

As shown in FIG. 2(4), when the control unit 5 changes the auxiliary relay signal from low level to high level (instruction to close) at t1, the AND circuit 23 of the rush current prevention circuit 20 changes the polarity signal from low level to high level at t2. When the trigger signal changes to high level, that is, at the zero cross point and at the start of the positive half cycle, the trigger signal is changed from low level to high level. The delay circuit 22 to which this trigger signal is input changes the drive signal from low level to high level at t3, which is delayed by 5 milliseconds from t2, as shown in FIG. 2(5).

The auxiliary relay 25 to which this drive signal is input starts a mechanical operation to connect the contacts, but the contacts are closed at t5 after the mechanical delay time (10 milliseconds) has passed as described above. However, this contact is completely closed at t6 when the chattering period has passed. From t7, which is the next positive half cycle, a current (rush current) begins to flow through the rectifier 2 as shown in FIG. 2(7). However, the current flowing after t7 rises smoothly because the AC voltage increases according to the sine wave rising from zero volts. The peak current at this time is 15 amperes at t8. After that, the peak current is 15 amps for each positive half cycle.

The charge accumulated in the smoothing capacitor 7 at a certain voltage is fixed. Therefore, in order to accumulate this charge in a short period of time, a large current is used to accumulate the charge at once. Therefore, the peak current increases. However, the amount of current that can flow is determined by the characteristics of the capacitor. On the other hand, when accumulating over a long period of time, gradual accumulation should be performed with a small current. In this embodiment, the current flowing into the smoothing capacitor 7 gradually increases as the instantaneous value of the AC voltage increases from zero volts. That is, since the current flowing to the smoothing capacitor 7 is temporally dispersed, the peak current can be suppressed.

On the other hand, as shown in FIG. 2(8), when the conventional circuit (diode 24 is not installed) is used, the contact of the sub-relay 25 is first closed at t5 when the peak voltage is reached in the negative half cycle. In this case, the inrush current is 20 amperes at peak current. Furthermore, contact current flows multiple times due to contact chattering. Therefore, it is necessary to employ a relay having a larger contact current than the relay used in this embodiment.

As described above, the inrush current prevention circuit 20 closes the sub relay 25 during a period in which no current flows through the diode 24 connected in series with the sub relay 25, thereby reducing the inrush current to the smoothing capacitor 7. can do. Therefore, it is possible to employ a relay with a smaller contact current than a relay used in a conventional inrush current prevention circuit.

1a input terminal 1b input terminal 2 rectifier 3 switching unit 3a inductor 3b diode 3c IGBT
3e input terminal 3f output terminal 3g common terminal 3h input terminal 4 main relay 5 control unit 6a output terminal 6b output terminal 7 smoothing capacitor 20 rush current prevention circuit (rush current prevention means)
21 voltage polarity detector 22 delay circuit 23 AND circuit 24 diode 25 auxiliary relay 26 resistor 30 power supply

Claims (1)

A pair of input terminals to which an AC power supply is connected, a rectifier for rectifying the AC voltage applied to the input terminals, a smoothing capacitor for smoothing the rectified voltage,
inrush current prevention means connected in series between one of the pair of input terminals and the rectifier to suppress inrush current flowing through the smoothing capacitor;
A power supply device comprising a control unit that outputs a control signal to the inrush current prevention means,
The inrush current prevention means is
A mechanical relay, a diode, and a resistor connected in series between one of the pair of input terminals and the rectifier, and detecting the polarity of the AC voltage applied to the pair of input terminals as a polarity signal and a voltage polarity detection unit that outputs
the relay is opened and closed by the control signal;
The inrush current prevention means is
When the control signal for closing the relay is input,
The relay is delayed by a predetermined time from the zero cross point detected by the polarity signal so that the timing at which the contact of the relay is closed is within the period of the polarity of the AC voltage that becomes the reverse voltage in the diode. A power supply device characterized by outputting a drive signal for closing the relay to the relay.

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